Composition for increasing cellulosic product strength and method of increasing cellulosic product strength

ABSTRACT

A composition includes water; at least one hydrophilic polymer containing at least two groups which are independently the same or different a primary amine group or a secondary amine group and at least one saccharide containing a reducible function as described above. The hydrophilic polymer and the saccharide are mixed to form a reaction mixture and reacted to increase the viscosity of the reaction mixture. The reaction is then substantially terminated by reducing the pH of the composition. A method of increasing the strength of a cellulosic pulp product includes the steps of: contacting wet cellulosic pulp with a composition comprising (i) at least one hydrophilic polymer containing at least two groups which are independently the same or different a primary amine group or a secondary amine group and at least one saccharide containing a reducible function, the hydrophilic polymer and the saccharide of the composition having been reacted in a crosslinking reaction prior to contacting the composition with the cellulosic pulp product to increase the viscosity the composition; and, after contacting the cellulosic pulp with the composition, causing the crosslinking reaction between the hydrophilic polymer and the saccharide of the composition to proceed further.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation in part application of U.S. patentapplication Ser. No. 10/252,262, filed Sep. 23, 2002 now U.S. Pat. No.7,090,745, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/410,375, filed Sep. 13, 2002, the disclosures ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to crosslinking compositionssuitable, for example, to increase the strength (that is, wet and/or drystrength) of cellulosic products (including, for example, paper andother products made from cellulosic pulp) and to methods of increasingthe strength of cellulosic products using such compositions.

For many years, the paper-making industry has sought ways of increasingthe strength of paper. In that regard, papers fabricated without someadditional means of reinforcement thereof can fall apart upon wetting orwhen subjected to mechanical stress in the dry state. Typically, amaterial is added to the wet pulp to improve the strength thereof duringthe formation of sheets prior to ultimate drying. Maintaining paperstrength upon wetting is desirable in many applications, includingbathroom tissue, paper towels, napkins, and the like. Moreover,additives which increase the strength of a wet paper often increase thedry strength of that paper. Increased dry strength is desirable, forexample, in various packaging applications.

A number of wet- and dry-strength increasing additives are known in theart. However, such compositions typically include one or more componentswhich are environmentally unfriendly or even toxic.

For example, some wet-strength additives are condensation products ofurea and formaldehyde. Polyamine can be added to make such resinscationic. Other wet-strength additives include organochlorinecrosslinked amidoamine compounds. A discussion of wet-strength additivesand their mechanisms is presented in “The 65 Mechanism of Wet-StrengthDevelopment in Paper: A Review,” by Herbert H. ESPY, Tappi Journal, Vol.78, No. 4, pages 90-97 (April 1995 as well as in “Chemistry of PaperWet-Strength. I. A Survey of Mechanisms of WetStrength Development,” byLars WESTFELT, Cellulose Chemistry and Technology, Vol. 13, pages813-825 (1979), the contents of which are incorporated by reference asthough set forth in full herein.

Chemical compositions purported to increase paper wet strength whilebeing chemically benign or environmentally friendly are set forth inU.S. Pat. No. 6,146,497, which describes a composition including (a) awater-soluble polymeric material comprising at least one nucleophilicpolymer, (b) a phenolic compound (phenols or polyphenols) and (c) acomponent (an oxidizing agent) capable of converting the phenoliccompound into a quinone compound. Sugars in conjunction with theircorresponding oxidases are contemplated as potential oxidizing agentsfor the phenolic component of the composition of U.S. Pat. No.6,146,497. Many phenolic compound, however, are environmentallyundesirable. Moreover, many oxidizing agents are also environmentallyundesirable (for example, potassium dichromate and potassiumpermanganate).

It thus remains desirable to develop improved, environmentally friendlycompositions for increasing paper wet and/or dry strength.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a composition comprisingat least one hydrophilic polymer containing primary (—NH₂) and/orsecondary (—NHR) amine groups (that is, hydrophilic polymer contains orincludes at least two groups which are independently the same ordifferent a primary amine group or a secondary amine group) and at leastone saccharide containing a reducible function. In general, the Rsubstituent upon the secondary amine is not limited. Strong electronwithdrawing groups are not preferred as such groups can reduce thenucleophilic nature of the secondary amine. In many cases, R is an alkylgroup. The amine groups can be pendant groups on the polymer orincorporated into the polymer backbone. In general, the hydrophilicpolymer must include at least two amine groups (per a polymer chain) toenable crosslinking.

Such an amine functional polymer/reducible saccharide combination hasbeen found to undergo an unexpected cross-linking reaction upon theapplication of heat. The compositions of the present invention can, forexample, be used as cross-linking agents in paper strengtheningapplications. As used herein, the term “polymer” refers to a compoundhaving multiple repeat units (or monomer units) and includes the term“oligomer,” which is a polymer that has only a few repeat units. Theterm polymer also includes copolymers which is a polymer including twoor more dissimilar repeat units (including terpolymers—comprising threedissimilar repeat units—etc.). The polymers used in the compositions ofthe present invention can be homopolymers and/or copolymers.

Hydrogels have found use in the paper industry, for example, asabsorbent materials. In that regard, hydrogels have been used asabsorbent materials in diapers for a number of years. Surprisingly, thepresent inventors have discovered that the compositions of the presentinvention, which form hydrogels, can also be used to increase both thewet strength and dry strength of paper and other cellulosic products.While the hydrophilic polymers of the present invention form hydrogelswith reducing sugars in aqueous solution, cross-linking can becontrolled (for example, by control of temperature as described below)allowing application of the hydrophilic polymer and the saccharide towet pulp (that is, paper or cellulosic fibers) and binding to the pulpprior to substantial cross-linking. Typically, a pre-formed hydrogelwould not be able to effectively bind to cellulosic fibers as a resultof its high viscosity.

Polymers suitable for use in the present invention include, but are notlimited to, partially hydrolyzed poly(N-vinylformamide) (that is, acopolymer of NVF and vinylamine), partially hydrolyzed vinyl acetate/NVFcopolymer (that is, a polymer with vinyl acetate, vinyl alcohol, NVF andvinylamine repeat units); hydrolyzed acrylonitrile/NVF copolymer;(available as a commercial product from Mitsubishi and containingacrylonitrile, acrylamide, amidine, NVF and vinylamine units), aminefunctional polyacrylamide (for example, prepared via Hoffman degradationof polyacrylamide), acrylic acid/vinylamine copolymer, maleicanhydride/maleic acid copolymers with NVF/vinylamine, NVF/vinylaminepolymers with vinyl sulfonate comonomer units, NVF/vinylamine copolymerswith cationic monomers such as diallyldimethylammonium chloride and/orcationic acrylate comonomers, allylamine/diallylamine polymers andcopolymers, urea/formaldehyde and melamine/formaldehyde condensationpolymers, amidoamine polymers (prepared from dicarboxylic acids andpolyfunctional amines), amine/epichlorohydrin polymers,poly(ethyleneimine), and hydrolyzed or partially hydrolyzedpoly(2-alkyl-2-oxazoline). One hydrophilic polymer or a mixture of twoor more such polymers can be used in compositions of the presentinvention.

In general, polymers having a broad range of number average molecularweight (Mw) are suitable for use in the present invention. Preferably,the molecular weight of the polymers is at least approximately 500. Morepreferably, the molecular weight is in the range of approximately 30,000to approximately 100,000. Polymers having molecular weight in excess of100,000 can be used, but water solubility can decrease for such polymersas molecular weight increases beyond approximately 100,000.

The reducible saccharides used in the present invention can bemonosaccharides, disaccharides, trisaccharides etc, (for example,sugars) or polysaccharides (for example, starch or cellulose).Polysaccharides are typically a combination of nine or moremonosaccharides. Reducible saccharides or reducing saccharides include areducing group, function or functionality which is typically an aldehydegroup (—C(O)H) or a hemiacetal group

which is another form of an aldehyde when the saccharide is in a cyclicconformation. Examples of reducing saccharides suitable for use in thepresent invention include, but are not limited to, the sugars glucose,lactose, and 2-deoxy-D-ribose. To decrease costs, the saccharide ispreferably a monosaccharide (for example, glucose), a disaccharide (forexample, lactose) or a polysaccharide (for example, starch).

The composition can, for example, further include a base. Examples ofsuitable bases include, but are not limited to, sodium hydroxide,potassium hydroxide, ammonia or calcium carbonate.

In one embodiment, the polymer is a copolymer of vinyl amine and vinylalcohol. Preferably, the copolymer is at least 0.5% by weight of vinylamine. More preferably, the copolymer is at least 3% by weight of vinylamine. Even more preferably, the copolymer is at least 6% by weight ofvinyl amine. Copolymers having well in excess of 6% by weight of vinylamine are suitable for use in the present invention. In severalembodiments for example, copolymer can be at least 12% by weight ofvinyl amine.

A broad range of mole ratios of amine to reducing saccharide is suitablefor use in the present invention. In one embodiment, the mole ratio ofamine groups to reducing saccharide is in the range of approximately 1:4to approximately 8:1. More preferably, the mole ratio of amine groups toreducing saccharide is in the range of approximately 1:2 toapproximately 8:1. In general, increasing amine content results instiffening of the resultant gel. One skilled in the art can readilydetermine an appropriate amine content for a desired set of propertiesfor the resultant gel.

In another aspect, the present invention provides a compositionincluding water; at least one hydrophilic polymer containing at leasttwo groups which are independently the same or different a primary aminegroup or a secondary amine group and at least one saccharide containinga reducible function as described above. In this aspect of the presentinvention, the hydrophilic polymer and the saccharide are mixed to forma reaction mixture and reacted (that is, crosslinked) until or so thatthe viscosity of the composition increases. The crosslinking reaction isthen substantially terminated (prior to completion) by reducing the pHof the composition (for example, by adding an acid such a aqueoushydrochloric acid). The viscosity of the composition can, for example,be at least 20 cp at 80° C. when the crosslinking reaction isterminated. In one embodiment, the viscosity of the composition is inthe range of approximately 20 cp to 100 cp at 80° C. when the reactionis terminated. The viscosity of the composition can further, be in therange of approximately 20 cp to 60 cp at 80° C. when the reaction isterminated. The viscosity of the composition can also be in the range ofapproximately 20 cp to 40 cp at 80° C. when the reaction is terminate.Preferably, the viscosity of the reduced pH composition is no greaterthan 80 cp at room temperature (that is, approximately 22° C.).

The pH of the composition can, for example, be greater than 7 duringreaction and reduced to less than 7 to substantially terminate thereaction. Preferably, the pH of the composition is at least 10 (and,more preferably, in the range of approximately 10 to 12) during reactionand reduced to 6 or less to substantially terminate the reaction. In oneembodiment, the pH of the composition is reduced to a pH in the range ofapproximately 4 to 6 to substantially terminate the reaction. In anotherembodiment, the pH of the composition is reduced to a pH in the range ofapproximately 5 to 6 to substantially terminate the reaction. Thecompositions of the present invention can be stored for extended periodsof time at a pH of 6 or less (and, for example, at room temperature)prior to causing further crosslinking (for example, in the strengtheningof paper).

In another aspect, the present invention provides a method of increasingthe strength of a cellulosic product including the step of contacting awet cellulosic pulp with a composition as described above. In oneembodiment, wet cellulosic pulp (for example, wet paper pulp) and thecomposition are contacted at a temperature below approximately 50° C.,or more typically, at room temperature or below (that is, atapproximately 25° C. or below) and subsequently heated to inducecross-linking. For example, the cellulosic pulp and the composition canbe heated to a temperature of at least 50°, at least 70° or at least90°.

In still a further aspect, the present invention provides a method ofincreasing the strength of a cellulosic pulp product including the stepsof: contacting wet cellulosic pulp with a composition comprising (i) atleast one hydrophilic polymer containing at least two groups which areindependently the same or different a primary amine group or a secondaryamine group and at least one saccharide containing a reducible function,the hydrophilic polymer and the saccharide of the composition havingbeen reacted in a crosslinking reaction prior to contacting thecomposition with the cellulosic pulp product to increase the viscositythe composition; and, after contacting the cellulosic pulp with thecomposition, causing the crosslinking reaction between the hydrophilicpolymer and the saccharide of the composition to proceed further.

In one embodiment, prior to contacting the wet cellulosic pulp with thecomposition, the hydrophilic polymer and the saccharide are mixed toform a reaction mixture and reacted (that is, crosslinked) until theviscosity of the composition increases. The reaction is thensubstantially terminated by reducing the pH of the composition asdescribed above. Upon addition of such compositions to wet cellulosicpulp, a further crosslinking (and a resultant further increase inviscosity) is promoted by a basic environment and heating. Afteraddition of the composition to the wet cellulosic pulp and furthercrosslinking, the wet cellulosic pulp is dried to form a cellulosic pulpproduct (for example, paper, tissue, cardboard etc.).

In still another aspect, the present invention provides a compositionformed from a mixture of water, cellulosic pulp, at least onehydrophilic polymer containing at least two groups which areindependently the same or different a primary amine group or a secondaryamine group and at least one saccharide containing a reducible function.

The compositions and methods of the present invention substantiallyincrease both the wet and dry strength of paper and other cellulosicproducts. The compositions can also be used as, for example,strengthening additives in other materials. The compositions of thepresent invention can be added to the cellulosic fibers as individualcomponents or as a pre-gel made by the partial reaction of thepolymer(s) or copolymer(s) and the reducible saccharide component(s). Nooxidizing agents, phenolic compounds, formaldehyde or organohalocompounds are required in the compositions and methods of the presentinvention. In general, no environmentally undesirable components areused in the compositions and methods of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a study of gel time at various temperatures for acomposition including a copolymer of vinyl amine and vinyl alcohol (6 wt% vinyl amine) and D-glucose at a 1:1 sugar/copolymer ratio.

FIG. 2 illustrates the effect of addition of base upon gel time.

FIG. 3 illustrates a study of gel time at various sugar:copolymer ratiosfor a composition including a copolymer of vinyl amine and vinyl alcoholand D-glucose.

FIG. 4 illustrates a study of gel time at various sugar:copolymer ratiosfor a composition including a copolymer of vinyl amine and vinyl alcoholand lactose.

FIG. 5 illustrates the viscosity of a composition including a copolymerof vinyl amine and vinyl alcohol (6 wt % vinyl amine) and D-glucose at a1:1 sugar/copolymer ratio as a function of time.

FIG. 6 sets forth a schematic representation of a Maillard reaction.

DETAILED DESCRIPTION OF THE INVENTION

As discussed above, during paper processing, material is added to thewet pulp to improve the strength during the formation of sheets prior toultimate drying. Preferably, the additive material or compositionexhibits a relatively low viscosity during addition (to fully absorbinto the pulp), then cures as temperature increases. Because paper comesinto intimate contact with people, the strength-enhancing material ispreferably relatively environmentally benign.

In the present invention, environmentally friendly or benigncompositions are used to increase the wet strength (as well as the drystrength) of paper. When individual polymer chains interact, chemical orphysical crosslinking may occur. This crosslinking results in athree-dimensional highly branched network of polymers.

When these networks become swollen with water they form hydrophilicgels, known as hydrogels. Hydrogels possess unique physical propertieshaving attributes of both solids and liquids. Solid-like properties canbe attributed to the strength of the crosslinked polymer networks.Whereas, fluid like properties result from the fact that the hydrogel istypically composed of over 80% water. The dual nature of their physicalproperties makes hydrogels particularly interesting and useful, in bothindustry and research.

The present inventors have discovered that water soluble polymers havingprimary and/or secondary amine groups undergo a crosslinking reaction inthe presence of a reducing saccharide such as a reducing sugar. Reducingsugars are sometimes referred to herein simply as sugars.

Several examples of the present invention are described usingcompositions including polymers with vinyl amine repeat groups and atleast one of several reducing sugars. Vinyl amine homopolymer was foundto form crosslinked polymer networks or gels in the presence of areducing sugar. Moreover, copolymers of vinyl amine and at least oneother monomer were also found to form crosslinked polymer networks orgels in the presence of a reducing sugar. In many instances, use of acopolymer of vinyl amine and at least one other monomer is preferable touse of a vinyl amine homopolymer in the present invention given theexpense of the vinyl amine monomer. In a number of studies of thepresent invention, representative copolymers of vinyl amine and vinylalcohol were used. Such copolymers are also sometimes referred to hereinas poly(vinylalcohol)/poly(vinylamine) or PVOH/PVAm copolymers.

Aqueous solutions of poly(vinylalcohol)/poly(vinylamine) copolymer and anumber of sugars were found to gel readily at temperatures betweenapproximately 50 and 100° C. In a series of initial experiments, knownamounts of sugars were mixed with a copolymer of vinyl amine and vinylalcohol (12 wt % vinyl amine) to form a 40% solution (in water) byweight. The mixtures were heated to various temperatures and held forvarying lengths of time. Gelation was determined to be the point where aTeflon stir bar ceased to move.

Vinyl amine is required for gelation to occur. In that regard,homopolymers of vinyl alcohol did not gel in the presence of sugar atelevated temperature. Homopolymers of vinyl amine or copolymers of vinylamine and vinyl alcohol gelled readily under these conditions. Reducingsaccharide (for example, sugar) is also required for gelation—vinylamine homopolymers and copolymers of vinyl amine and vinyl alcohol didnot gel without the presence of sugar. Gelation occurs over a wide rangeof amine:sugar (saccharide) ratios.

Gelation occurred in the presence of 2-deoxy-D-ribose, suggesting thatthe osazone mechanism was not responsible for crosslinking. On the otherhand, gelation did not occur when using sucrose, suggesting thatMaillard chemistry (known from food chemistry) is involved in thecrosslinking and hence gelation. Prior studies suggest that nomutagenicity results from products of the Maillard reaction whendisaccharides are employed. Lactose, for example, allows for gelation inthe compositions and systems of the present invention. Although it isbelieved that the Maillard chemistry is involved in gelation in thecompositions of the present invention, the present invention is notlimited to any particular mechanism of gelation.

Increasing temperature increases the rate of the reaction/gelation. Inseveral experiments with a 12% (wt) amine sample, for example, the timefor gelation dropped with increasing temperature from 335 minutes (50°C.) to 113 minutes (60° C.) to 50 minutes (70° C.) to 24 minutes (80°C.) to less than 10 minutes at (90° C.). FIG. 1 illustrates graphicallythe effect of increasing temperature on gel time for a copolymer ofvinyl amine and vinyl alcohol having 6% (wt) vinyl amine. Addition ofacid (for example, H₂SO₄) slowed the gelation reaction, while additionof a base (for example, NaOH) accelerated the gelation reaction (seeFIG. 2).

FIGS. 3 and 4 illustrate studies of the effect of mole ratio of sugar tocopolymer (6% by weight amine) for D-glucose and lactose, respectively.In general, sugar concentration only slightly effected gel time.Moreover, the type of sugar used did not greatly affect gelation time.Lactose was found to be slightly better than D-glucose in these studies.

A number of experiments were performed to explore the ability of the gelto strengthen wet paper, as summarized below. The PVOH/PVAm:glucose 2:1sample clearly showed improved wet strength over PVOH/PVAm without sugarand is substantially superior to the control paper and to glucose coatedpaper. These results demonstrate the effectiveness of the compositionsof the present invention in improving the wet strength and the drystrength of paper. The temperature dependence of the rate ofcross-linking of the compositions of the present invention allows timeto apply the relatively low-viscosity mixtures of hydrophilic polymerand reducing saccharide of the present invention to pulp fibers, withstrength properties developing in the finished sheet. Dehydrationreadily occurs in the paper sheet upon drying to form a strengtheningcross-linked matrix.

In the experiments of Tables 1 and 2, a sample of PVOH/PVAm (12 wt %vinyl amine; medium molecular weight) was dissolved at 4 wt % indistilled water. A sample of glucose was also dissolved at 4 wt % indistilled water. These samples were applied to Whatman #4 filter paperto provide even coverage.

TABLE 1 Dry Result Coat Weight (weight of coating/ Dry Strength SampleDescription weight of paper) (lbs) Control Paper 0 5.43 PVOH/PVAm 0.12415.3 Glucose 0.137 4.1 PVOH/PVAm:glucose 2:1 0.118 11.7

TABLE 2 Wet Results Coat Weight (weight of coating/ Wet Strength SampleDescription weight of paper) (lbs.) Control Paper 0 0.095 PVOH/PVAm0.085 0.81 Glucose 0.134 0.128 PVOH/PVAm:glucose 0.081 3.26

In several other experiments, a sample of PVOH/VAm (12 mole % vinylamine repeat units) was dissolved at 6 wt % in distilled water. In theseexperiments, the composition including the hydrophilic polymer PVOH/PVAmand a reducing sugar (for example, D-glucose) was reacted prior tocontact with a wet cellulosic pulp to first increase the viscosity ofthe composition. Increasing the viscosity of the composition can, forexample, result in better binding of the composition to the wetcellulosic pulp. The crosslinking reaction can be terminated prior tocompletion by, for example, reducing the pH of the composition throughthe addition of an acid. Preferably, the pH of the composition isreduced to a pH in the range of 4 to 6. It was discovered that, thecompositions of the present invention can be stored for extended periodsof time at a pH of 6 or less without substantial further crosslinkingreaction. Upon addition of such compositions to wet cellulosic pulp, afurther crosslinking (and a resultant further increase in viscosity) ispromoted by a basic environment and heating. The compositions of thepresent invention can, for example, be added to wet cellulosic pulp inthe range of approximately 0.05 to 2 wt % on the basis of the weight drycellulosic pulp. The compositions of the present invention can also beadded in the range of approximately 0.1 to 1 wt % based upon the weightof the dry cellulosic pulp. The compositions of the present inventioncan further be added in the range of approximately 0.1 to 0.5 wt % basedupon the weight of the dry cellulosic pulp.

Experimental

Materials. All chemicals were used without further purification.Poly(vinylalcohol) (98-99%, M_(w) 31,000-50,000), D-glucose (A.C.S.reagent) and 2-deoxy-D-ribose (97%) were purchased from Aldrich ChemicalCo. Sucrose (A.C.S. reagent) was purchased from J. T. Baker Chemical.Lactose (A.C.S. reagent) was purchased from E.M. Science. L-ribose(99.5%) was purchased from Acros Organics. Thepoly(vinylalcohol)/poly(vinylamine) copolymers (6 and 12% amine, mediumM_(w)) were donated by Air Products and Chemicals Inc.

Instrumentation. Infrared spectra (IR) were obtained on an ATI MattsonFTIR spectrometer. Information obtained was used to determine chemicalchanges occurring during gelation.

Synthesis of poly(vinylamine). Poly(vinylamine) was synthesized usingN-vinyl formamide (NVF). First poly(vinylformamide) (PNVF) was made bycombining 100 mL of the NVF monomer, 40 mL of DMSO solvent, 61 mg Vazo88 initiator (cyclohexane carbonitrile), and 0.5 g RAFT agent in athree-neck flask. The mixture was then heated at 100° C. for ˜2 hoursunder nitrogen gas with constant stirring and with reflux conditions.After heating, the product was diluted in a 50 mL/50 mL water/ethanolmixture. The product was then precipitated out of solution usingacetone. Product was dried overnight in a vacuum oven, redisolved in a120 mL/50 mL water/ethanol mixture and subsequently precipitated usingacetone. The PNVF was hydrolyzed under basic conditions by combining thepolymer, concentrated NaOH (5% excess) and distilled deionized water ina round bottom flask. The mixture was then heated at 80° C. for 18hours, under reflux conditions and with constant stirring. Adding HCl tothe cold product solution precipitated the product. The product was thenwashed with methanol three times and dried in a vacuum oven. HCl wasremoved by adding aqueous NaOH. This product was precipitated inacetone, dried and then washed with butanol.

EXAMPLES Example 1

An aqueous solution was prepared by dissolving 7.5 g D-glucose and 2.5 gpoly(vinylalcohol) (PVOH) into distilled, deionized water in a 25 mLvolumetric flask. The solution was clear with some undissolved polymer.It was, however, pourable. The solution was transferred to a roundbottom flask and heated to 80° C. in an oil bath. Heating was done withconstant stirring and under reflux conditions. Upon completion thesolution remained clear with all polymer dissolved and was stillpourable.

Example 2

Prior studies suggest that an aqueous solution of PVOH and D-glucosecould be used to form hydrogels by using freezing/thawing cycles. SeeYamaura, K.; Fukada, M.; Tanaka, T.; Tanigami, T. J. of Applied PolymerScience. 1999, 74, 1298-1303. To study this effect, a solution wasprepared as in example 1. Heating was carried out using the sameprocedure as in example 1, but was allowed to reach a temperature of 90°C. The aqueous solution was then placed in a −10° C. freezer over 48hours. After thawing the solution at room temperature for 1 hour a weak,white hydrogel had formed. The gel was then placed back in the freezerfor 24 hours and then thawed at room temperature for 1 hour. Afterwhich, the gel appeared visibly stronger. This gel was found to besoluble in water heated up to 49° C. Neither swelling nor dissolutionwas noted when placed in 1M HCl.

Example 3

Prior studies further suggest that D-glucose was not necessary for thegelation of poly(vinylalcohol) using the process in example 2. SeeYamaura, K.; Karasawa, K. I.; Tanigami, T.; Matsuzawa, S. J. of AppliedPolymer Science. 1994, 51, 2041-2046. To study such gelation, a 2.5 g ofPVOH was dissolved in distilled, deionized water in a 25 mL volumetricflask. Heating was carried out using the same procedure as in example 1,but was allowed to reach a temperature of 95° C. The solution was thenplaced in the freezer at −25° C. for 48 hours. After 1 hour of thawingat room temperature a gel, similar in appearance to the gel in Example2, was produced. The inability of PVOH to form hydrogels without thefreezing/thawing cycle indicated that the amine groups on copolymers ofPVOH and Poly(vinylamine) in the compositions of the present inventionare responsible for gelation.

Example 4

Poly(vinylamine) (PVA) was also used in trying to make gels. An excessof PVA was used in the case that some butanol was still present in thesynthesized polymer. 2.8 g of PVA was dissolved in distilled, deionizedwater in 25 mL volumetric glassware leaving room for the addition ofD-glucose and more water. A heating gun was used, as needed, to dissolvepolymer. D-glucose was dissolved in some water in a separate container,added to the other solution and diluted as necessary. This solution wasorange in color and pourable. Heating was carried out using the sameprocedure as in example 1, but was allowed to reach a temperature of100° C. A rubbery, dark brown gel began to appear at ˜95° C. This gelswelled when exposed to both excess water and 1M HCl.

Example 5

To ensure that the discoloration observed in Example 4 was a result ofgelation and not merely oxidation of the amine, Example 4 was repeatedunder nitrogen gas. This was done using a three neck flask, rubberseptum and needle. The rubbery, dark brown gel appeared at ˜93° C.again. This gel was slightly lighter in color than the gel of Example 5.This gel swelled in water and in 1M HCl.

Example 6

To study whether a sugar was necessary for gelation, 1.25 g of PVA wasdissolved in water in a 25 mL volumetric flask. This solution was thenheated to 95° C. using the procedure of Example 1. No gelation wasobserved.

Example 7

The poly(vinylalcohol)/poly(vinylamine) copolymer that was used for theexperiments set forth in Examples 7 through 24 contained 12% aminegroups. 2.5 g of the copolymer followed by 7.5 g of D-glucose weredissolved in distilled deionized water using the procedure outlined inExample 4. This solution was then transferred to a three-neck flask andheated in an oil bath to 100° C. Heating was carried out under refluxconditions, with constant stirring and under argon gas. A strong, brightyellow gel appeared at ˜90° C. This gel swelled when exposed to excesswater and to 1M HCl.

Example 8

The procedure in example 7 was repeated using 2.5 g D-glucose. This is a1:2 mole ratio of amine groups to sugar molecules. Gelation began tooccur at ˜90° C. This gel was strong and yellow. It swelled in water and1M HCl.

Example 9

The procedure of Example 7 was repeated using 1.25 g D-glucose (a 1:1mole ratio of amine groups to sugar molecules). Gelation began to occurat ˜90° C. This gel was a pale yellow color. This gel is still strongbut not as strong as the previous two examples. Swelling was noted inwater and 1M HCl. IR spectra were taken of the aqueous solution beforeheating and of this gel afterwards. Before heating a strong peak wasseen around 1680 cm⁻¹, which is typical of a primary amine peak. Afterheating this peak became much smaller, more typical of a secondaryamine. Another unidentified peak appeared after heating at ˜1090 cm⁻¹.

Example 10

The procedure of Example 7 was repeated using 0.61 g D-glucose (a 2:1mole ratio of amine groups to sugar molecules). Gelation began to occurat ˜95° C. This gel was strong yet somewhat sticky and a clear yellowcolor. Swelling was noted when exposed to water and to 1M HCl.

Example 11

The procedure of Example 7 was repeated using 0.31 g D-glucose (a 4:1mole ratio of amine groups to sugar molecules). Gelation began to occurat ˜100° C. The gel produced was sticky and almost clear in color. Thisgel swelled when exposed to excess water and to 1M HCl.

Example 12

The procedure of Example 7 was repeated using 0.16 g D-glucose (a 8:1mole ratio of amine groups to sugar molecules). Gelation began to occurat ˜100° C. This gel was sticky and clear. Swelling occurred whenexposed to water and to 1M HCl.

Example 13

To test for the possibility of an osazone mechanism L-ribose was usedinstead of D-glucose. The procedure followed was similar to that ofexample 9 (using a 1:1 mole ratio and the same conditions). 1.02 g ofL-ribose was used. Gelation occurred at ˜85° C. This gel was strong,sticky and bright orange in color. This gel swelled when exposed toexcess water and to 1M HCl.

Example 14

As part of the aforementioned test of reaction mechanism2-deoxy-D-ribose was also used instead of D-glucose. The procedure ofExample 9 was once again followed, this time using 0.91 g of2-deoxy-D-ribose. Gelation occurred at ˜85° C. This gel was also strongand bright orange. The gelation of 2-deoxy-D-ribose indicates that theosazone reaction is not taking place since it would be unable to occuras a result of the structure of this sugar. Without limitation to anyparticular reaction mechanism in the present invention, a Maillardreaction mechanism is thus indicated. The gel of this example swelledwhen exposed to excess water and to 1M HCl.

Example 15

Prior studies show that little or no mutagenicity results from theMaillard reaction when disaccharides, such as lactose, are involved.See, for example, Brands, C. M. J.; Alink, G. M.; vanBoekel, M. A. J.S.; Jongen, W. M. F. J. Agric. Food Chem. 2000, 48, 2271-2275. A summaryof the Maillard reaction is provided in FIG. 6. Thus lactose is a goodsugar for use in the present invention. The procedure of Example 9 wasused, with 2.45 g of lactose. A strong, orange gel formed at ˜100° C.Solubility tests were not carried out on this gel.

Example 16

Sucrose is a disaccharide lacking active carbonyl groups. Therefore,sucrose would not be able to form a gel via the Maillard reaction. SeeBaynes, J. W.; Monnier, V. M. “The Maillard Reaction in Aging, Diabetesand Nutrition” 1989; and O'Brien, J.; Nursten, H. E.; Crabbe, M. J. C.;Ames, J. M. “The Maillard Reaction in Foods and Medicine” 1998. Theprocedure from example 9 was once again repeated. In this example, time2.33 g of sucrose was used. The temperature was taken up to 115° C. andgelation was not observed.

Example 17

Constant temperature experiments were also carried out. 2.5 g ofcopolymer followed by 1.25 g of D-glucose were dissolved in water usinga 25 mL volumetric flask as outlined in Example 4. Heating took place inan oil bath that was maintained at a constant temperature of 80° C.Heating was done under reflux conditions, under argon gas and withconstant stirring. Gelation time was noted as the time when the gelbecame too viscous for the stir bar to move. In this example gelationtime was found to be 23.5 minutes. The gel produced was a clear yellowand sticky. This gel dissolved in water.

Example 18

The procedure of Example 17 was repeated using an oil bath at 70° C.Gelation time was noted as 49.5 minutes. This gel was weaker andstickier than the previous one. This gel also dissolved in water.

Example 19

The procedure of Example 17 was repeated using an oil bath at 60° C.Gelation time was noted as 113.25 minutes. This gel was weaker andstickier than the previous one. This gel also dissolved in water.

Example 20

The procedure of Example 17 was repeated using an oil bath at 50° C.Gelation time was noted as 335.0 minutes. This gel was weaker andstickier than the previous one. This gel also dissolved in water.

Example 21

To test the effect of pH on gelation, the procedure of Example 17 wasrepeated under acidic conditions. Three drops of concentrated H₂SO₄ wereadded to the aqueous solution. After 120.0 minutes the solution hadturned slightly yellow and appeared to be a pourable gel. This gel wasalso soluble in water.

Example 22

Basic conditions were also examined using the procedure in example 17.0.04 g of concentrated NaOH were added to the aqueous solution. Gelationwas noted after 18.2 minutes. This gel was similar in appearance to thatproduced in Example 17. This gel was slightly soluble in excess water.

Example 23

The gels studied in FIGS. 1 through 5 were synthesized in a consistentmanner. In that regard, 21.25 grams of copolymer was weighed out into abeaker and set aside for both 6 wt % and 12 wt % amine copolymers. Thesugar was also weighed out in a beaker and set aside. The amount ofsugar added depended on the mole ratio of sugar to amine, which isindicated in Table 3 below for each ratio.

TABLE 3 Molar Ratio (sugar:amine) And Type of Sugar Amount of Sugar(grams) 1:1 glucose 5.23 2:1 glucose 10.46 4:1 glucose 20.92 1:2 lactose5.23 1:1 lactose 10.46 2:1 lactose 20.92The saccharide (sugar):amine rations set forth in Table 3 and FIGS. 3and 4 are merely the reciprocal of amine:sugar mole ratios.

Deionized water was measured out in a tall form beaker to approximately425 mL. A small amount (˜¼) of this water was put into another tall formbeaker and the sugar was added and mixed thoroughly. The bulk of thewater was used to mix with the copolymer. The mixture of copolymer/waterwas then put into an oil bath and mixed to allow the copolymer todissolve. Next, the sugar/water mixture was added into the copolymermixture and the time was started. The UL adapter was then lowered intothe mixture and the Brookfield viscometer was turned on to a speed of 60(The Brookfield viscometer had been earlier calibrated with water). Thereadings form the Brookfield were not recorded until after the time hadreached 9 minutes to allow the UL adapter to settle. The time was thenrecorded after each minute. The only other change in procedure occurredwhen the NaOH was added [50% (w/w/) NaOH in water solution]. 31 mM ofNaOH (or 1 gram of the NaOH in water solution) was added into thesugar/water mixture before adding it to the copolymer mixture.

Example 24

In several studies of the effect of the compositions of the presentinvention upon wet and dry strength of paper, a sample of PVOH/PVAm (12wt % VAm; medium molecular weight) was dissolved at 4 wt % in distilledwater. A sample of glucose was also dissolved at 4 wt % in distilledwater. These samples were applied to Whatman #4 filter paper from a 6″roll using a wire wound rod (RDS40) to provide even coverage. 50 gramsof the 4 wt % solution of PVOH/PVAm were mixed with 25 grams of the 4 wt% solution of glucose and also coated on the above noted filter paperusing a wire wound rod to provide even coverage. The samples were placedin an air circulating oven for 10 minutes at 100° C. The samples wereremoved and conditioned at 23° C.; 50°/″ RH for 16 hours prior totesting. 1″ wide strips were cut transverse to the filter paper rolldirection and cut into two 3″ long specimens for dry tensile testing.Samples were also cut into 3″ long specimens and immersed in water for30 seconds and tested for wet tensile strength. The results are setforth in Table 1 and 2 above. The sample weights were measured todetermine coat weights (amount of additive on the coated paper versusthe uncoated paper). Data on an average of four specimens is set forthin Tables 1 and 2. The testing rate was 2 in./min. strain rate (2 in.gage length).

Example 25

The polymer used in this example and the following examples was acopolymer of vinyl alcohol and vinylamine (PVOH/VAm), containing 12 mole% vinylamine repeat units, with a medium molecular weight. Although anyreducing sugar may be used, D-glucose was used in this and the followingexamples. Twelve (12) grams of PVOH/VAm were dissolved in 200 grams ofwater. The solution was heated to 90° C. and then filtered to remove anyinsoluble material. With the solution temperature maintained at 80° C.,six grams of D-glucose was added, followed by sufficient 30% sodiumhydroxide solution to bring the solution pH to at least 10, preferablyapproximately 12. With continued heating in the 80-90° C. range thesolution converts to a thick viscous gel. The relationship between timeto gelation and temperature is illustrated in Table 4 for thecrosslinking of PVOH/VAm with D-glucose at a 1:1 mole ratio and a pH of12.5.

TABLE 4 Temperature (° C.) Time to gelation 22 66 hours 30 28 hours 4022 hours 50 5 hours 60 40 minutes 80 10–20 minutes

Example 26

As in Example 25, twelve grams of PVOH/VAm were dissolved in 200 gramsof water, heated to 90° C. and filtered to remove insoluble material.Maintaining the solution temperature at 80° C., six grams of D-glucosewere added, followed by sufficient 30% aqueous sodium hydroxide to bringthe solution pH to at least 10. The initial viscosity was 17 cps. Afterapproximately twenty minutes at 80° C., the viscosity had risen to 40cps. Once the viscosity reached 40 cps, the solution pH was adjusted to6 by addition of 33% hydrochloric acid solution. The viscosity wasmeasured as 22 cps at 80° C. and 80 cps at 23° C. The solution does notgel and can be stored at room temperature for several weeks without anyevidence of gel formation.

Example 27

A dynamic handsheet maker (Techpap) was employed to make paper samplesfor testing. Sixteen (16) grams of dry cellulosic fiber were used tomake a slurry in water at 1% consistency. The pH of the slurry wasadjusted to the desired level and the acid-stabilized PVOH/VAm/D-glucosefrom Example 26 added at a level of 0.5 weight % (equivalent to 10lb/ton) based on the amount of dry fiber in the slurry. The rotationspeed of the handsheet maker was set at 680 rpm and pressure applied toform the paper sheet. The wet paper web was pressed and dried at 115° C.for eight minutes. The paper sheets were conditioned at 23° C. and 50%relative humidity for one day. The treated paper sheets were then testedfor wet tensile, dry tensile and burst strength using standard tests.The results were normalized to allow for differences in thickness andgrammage for each sheet.

Example 28

Paper sheets were made up as in Example 27, both with and without thepolymer additive. The PVOH/VAm/D-glucose solution was heated for 30minutes at 80° C. before adding to the fiber suspension. The finalviscosity (at room temperature) was 80 cps. The results are summarizedin Table 5.

TABLE 5 Additive None PVOH/VAm/D-glucose pH 5.5 5.5 DBL (km) 3.646 4.173WBL (km) 0.054 0.332 WBL/DBL (%) 1.5 8.00In Table 5, “DBL” refers to Dry breaking length, while “WBL” refers toWet breaking length

Example 29

Paper sheets were made as in Example 27, using the PVOH/VAm both withand without added D-glucose. The copolymer/glucose solution was heatedat 80° C. for 30 minutes before use and the final viscosity at roomtemperature was 68 cps. The results are summarized Table 6.

TABLE 6 Additive None PVOH/VAm PVOH/VAm/D-glucose pH 5.5 8 8 DBL (km)3.646 3.934 3.912 WBL (km) 0.054 0.326 0.361 WBL/DBL (%) 1.50 8.30 9.20

Example 30

Paper sheets were made as in Example 27, both with and without polymeradditive. The PVOH/VAm/D-glucose was heated at 80° C. until a finalviscosity of 225 cps (as measured at room temperature) was reached. Theresults are summarized in Table 7.

TABLE 7 Additive None PVOH/VAm/D-glucose pH 5.5 5.5 DBL (km) 3.646 4.39WBL (km) 0.054 0.352 WBL/DBL (%) 1.50 8.01

Example 31

Paper sheets were made as in Example 27, both with and without polymeradditive. The PVOH/VAm/D-glucose samples were heated for different timesat 60° C. prior to use. The results are summarized in Table 8.

TABLE 8 PVOH/ PVOH/ PVOH/ VAm/D- VAm/D- VAm/D- Additive None glucoseglucose glucose Reaction — 12 22 33 Time (mins) Viscosity (cps) — 53 7183 pH 5.5 5.5 5.5 5.5 DBL (km) 3.291 3.37 3.638 3.61 WBL (km) 0.0510.357 0.373 0.367 WBL/DBL (%) 1.5 10.6 10.3 10.2

Example 32

A paper-making trial was conducted on a pilot-scale paper machine. Themachine used was a Fourdrinier (width 25 inches), with a nominal paperoutput of 160 lbs paper per hour. The pulps used were old corrugatedcontainers (OCC) and a mix of OCC with recycled newsprint. Polymer wasadded in the range of 2-10 lbs/ton on a dry basis. Sample sheets werecut from the paper reel and conditioned in the same fashion as thehand-sheets in Example 27. Results were normalized for thickness andweight. The PVOH/VAm solution was prepared as in Example 26, filteredand stored in a drum. D-glucose was added to this stock solution, pHadjusted to 12 and the solution was then heated to 80° C., whilemonitoring viscosity. Measured viscosities were below 100 cps during useof the solution.

Example 33

Paper was made on the pilot machine using old corrugated containers(OCC) as the fiber source. The paper produced was 26-28 lbs per 1,000square feet, with a caliper of approximately 9.0. A base sheet wasproduced with no additive. Then PVOH/VAm/D-glucose (P) was fed to thepaper stock at a rate to give a 2 to 10 lb per ton (0.1-0.5%)application level on a dry basis. Results are summarized in Table 9.Properties reported were measured in the machine direction.

TABLE 9 P P P P Additive None (0.1%) (0.2%) (0.3%) (0.4%) P (0.5%) DBLkm 6.407 6.469 6.005 6.402 5.903 5.917 WBL (km) 0.38 0.25 0.45 0.50 0.470.51 WBL/DBL (%) 5.9 3.9 7.5 7.8 8.0 8.5 Burst Index 2.683 2.878 2.8042.787 2.711 2.597

Example 34

Paper was made as in Example 33, but using a mixture of OCC and oldnewsprint as fiber source. A base sheet was produced with no additive.Then PVOH/PVAm/D-glucose (P) was added at levels sufficient to give 6and 8 lb/ton (0.3 and 0.4%) application levels. Properties reported weremeasured in the machine direction and are summarized in Table 10.

TABLE 10 Additive None P (0.3%) P (0.4%) DBL (km) 5.598 5.654 5.715 WBL(km) 0.19 0.35 0.52 WBL/DBL (%) 3.4 6.2 9.1 Burst Index 2.489 2.4732.672

Example 35

The procedure of Example 34 was repeated, using PVOH/VAm/D-glucose (P)solution that had been aged for several hours to an increased viscosity.The polymer was added at levels sufficient to give 6 and 8 lb/ton (0.3and 0.4%) application levels. Properties reported were measured in themachine direction and are summarized in Table 11.

TABLE 11 Additive None P (0.3%) P (0.4%) DBL (km) 5.598 5.524 5.909 WBL(km) 0.19 0.47 0.58 WBL/DBL (%) 3.4 8.5 9.8 Burst Index 2.489 2.6762.837

The foregoing description and accompanying drawings set forth preferredembodiments of the invention at the present time. Various modifications,additions and alternative designs will, of course, become apparent tothose skilled in the art in light of the foregoing teachings withoutdeparting from the scope of the invention. The scope of the invention isindicated by the following claims rather than by the foregoingdescription. All changes and variations that fall within the meaning andrange of equivalency of the claims are to be embraced within theirscope.

1. A method of increasing the strength of a cellulosic pulp productcomprising: contacting wet cellulosic pulp with a composition comprising(i) at least one hydrophilic polymer containing at least two groupswhich are independently the same or different a primary amine group or asecondary amine group and at least one saccharide containing a reduciblefunction, the hydrophilic polymer and the saccharide of the compositionhaving been reacted in a crosslinking reaction prior to contacting thecomposition with the cellulosic pulp product to increase the viscositythe composition ,the crosslinking reaction being substantiallyterminated by changing at least one reaction condition; and, aftercontacting the cellulosic pulp with the composition, causing thecrosslinking reaction between the hydrophilic polymer and the saccharideof the composition to proceed further by providing reaction conditionssuitable to cause the reaction to proceed further.
 2. The method ofclaim 1, wherein prior to contacting the wet cellulosic pulp with thecomposition, the hydrophilic polymer and the saccharide are mixed toform a reaction mixture and reacted to increase the viscosity of thereaction mixture, the reaction then being substantially terminated byreducing the pH of the composition.
 3. The method of claim 1 wherein thepredetermined viscosity of the composition is at least 20 cp at 80° C.when the reaction is substantially terminated.
 4. The method of claim 1wherein the predetermined viscosity of the composition is in the rangeof approximately 20 cp to 100 cp at 80° C. when the reaction issubstantially terminated.
 5. The method of claim 1 wherein thepredetermined viscosity of the composition is in the range ofapproximately 20 cp to 60 cp at 80° C. when the reaction issubstantially terminated.
 6. The method of claim 1 wherein thepredetermined viscosity of the composition is in the range ofapproximately 20 cp to 40 cp at 80° C. when the reaction issubstantially terminated.
 7. The method of claim 1, wherein thepredetermined viscosity of the reduced pH composition is no greater than80 cp at 23° C.
 8. The method of claim 1 wherein the pH of thecomposition is greater than 7 during reaction and reduced to less than 7to substantially terminate the reaction.
 9. The method of claim 1wherein the pH of the composition is greater in the range ofapproximately 10 to 12 during reaction and reduced to 6 or less tosubstantially terminate the reaction.
 10. The method of claim 9 whereinthe pH of the composition is reduced to a pH in the range ofapproximately 4 to 6 to substantially terminate the reaction.
 11. Themethod of claim 9 wherein the pH of the composition is reduced to a pHin the range of approximately 5 to 6 to substantially terminate thereaction.
 12. The method of claim 1 wherein the reducing saccharide is amonosaccharide, a disaccharide or a polysaccharide.
 13. The method ofclaim 1 wherein the polymer is partially hydrolyzedpoly(N-vinylformamide), partially hydrolyzed vinylacetate/N-vinylformamide copolymer, hydrolyzedacrylonitrile/N-vinylformamide copolymer, amine functionalpolyacrylamide, acrylic acid/vinylamine copolymer, maleicanhydride/maleic acid copolymers with N-vinylformamide/vinylamine,N-vinylformamide/vinylamine polymers with vinyl sulfonate comonomerunits, an NVF/vinylamine copolymer with at least one cationic monomer,diallylamine polymer, allylamine/diallylamine copolymer,urea/formaldehyde condensation polymers, melamine/formaldehydecondensation polymers, amidoamine polymers, amine/epichlorohydrinpolymers, poly(ethyleneimine), hydrolyzed poly(2-alkyl-2-oxazoline) orpartially hydrolyzed poly(2-alkyl-2-oxazoline).
 14. The method of claim1 wherein the polymer is a copolymer of vinyl amine and at least oneother monomer.
 15. The method of claim 1 wherein the cellulosic pulp iscontacted with the composition in the presence of a base.
 16. The methodof claim 1 wherein the saccharide is at least one of glucose, lactose,or 2-deoxy-D-ribose.
 17. The method of claim 1 wherein wet cellulosicpulp and the composition are contacted at room temperature or below andsubsequently heated to induce crosslinking.
 18. The method of claim 1wherein the cellulosic pulp and the composition are heated to atemperature of at least 50° C.
 19. The method of claim 1 wherein thecellulosic pulp and the composition are heated to a temperature of atleast 70° C.
 20. The method of claim 1 wherein the cellulosic pulp andthe composition are heated to a temperature of at least 80° C.
 21. Themethod of claim 11 further including the step of drying the wetcellulosic pulp.
 22. The method of claim 13 wherein the polymer is anNVF/vinylamine copolymer with diallyldimehylammnonium chloride or with acationic acrylate comonomer.